What OS do you use pad? I tried FOREVER to get Dark Souls to work with DSfix on Windows 8, and it would just crash every time, no matter what I did. I haven't tried it with 8.1 yet, so maybe that will be the magic touch. Honestly though, the game ran fine for me without it, although not quite as pretty as I'm sure it would with it.
Still, it runs 1,000x better than the 360 copy, which hits single digit framerates sometimes, I swear.